This core is designed to provide centralized, specialized animal care for several breeding colonies (i.e., NOD/SCID, CD34 null, and wild type control mice). Breeding of thee mice is required for our studies as most of these strains are not commercially available in the quantities needed for our studies. The large number of recipients to be transplanted and monitored for engraftment is the other major function of this core. We believe providing the expertise centrally for this service is efficient both scientifically and financially. Finally, this core will provide genotyping for transgenic mice of several of our breeding colonies.